Solvent extraction process

ABSTRACT

A PROCESS FOR THE SOLVENT EXTRACTION OF A PLURALITY OF COMPONENTS FROM A PLURALITY OF HYDROCARBON STREAMS IN ACCORDANCE WITH THE CARBON-HYDROGEN RATIO OF THE COMPONENTS WHICH SEPARATES A FIRST STREAM COMPRISING HYDROCABONS OF THE GENERAL FORMULA CNH2N+2, AND A SECOND   STREAM COMPRISING HYDROCARBONS OF THE GENERAL FORMULA CNH2N AND A THIRD STREAM COMPRISING HYDROCARBONS IN WHICH THE HYDROGEN TO CARBON RATIO IS LESS THAN 2.

Jan. 11, 1972 J. F; HUTTO SOLVENT EXTRACTION PROCESS Filed ma 14, 1969 INVEHTOR. J. F HUTTO A T TORNEKS United States Patent 3,634,537 SOLVENT EXTRACTION PROCESS John F. Hutto, Bartlesville, Okla., assignor to Phillips Petroleum Company Filed May 14, 1969, Ser. No. 824,418 Int. Cl. C07c 7/10; C10g 21/28 U.S. Cl. 260-681.5 R 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved solvent extraction process.

In one of its more specific aspects, this invention relates to an improved process for the solvent extraction separation of a plurality of liquid hydrocarbons of contiguous boiling points.

Solvent extraction operations involve contacting a multi-component mixture with a solvent and recovering a raflinate and an extract. The rafiinate has a relatively high proportion of that material for which the solvent has a lesser afiinity, and the extract is comprised of the' solvent and a relatively high proportion of that material for which the solvent has the greater aflinity. The extract is separated into lean solvent and the extracted material, and the lean solvent is recycled to the contacting step.

Solvent extraction processes affect separation by preferential absorption and hence it is conventional to perform the individual extractions of any one group of homologs in a single zone. For example, it is conventional to conduct extractions of a C saturate and a C unsaturate in one zone, and the extraciton of C saturates and C unsaturates in a separate zone There has now been discovered a solvent extraction process by which multi-component separation can be performed in an efficient manner requiring fewer zones than heretofore required.

According to the method of this invention a plurality of hydrocarbon streams are passed successively in the order of increasing carbon content in contact with a solvent which has an increasing aflinity for those hydrocarbons having low carbon to hydrogen mol ratio and separating overhead a first hydrocarbon stream comprising hydrocarbons substantially of the formula C H and separating a second stream comprising hydrocarbons substantially of the formula C H and separating as an extract the solvent and a third stream substantially comprising hydrocarbons having hydrogen to carbon mol ratio of less than 2. The third hydrocarbon stream is then recovered from the solvent.

In one embodiment of this invention, the process is adapted to the separation of a plurality of hydrocarbons such as saturated, monoolefinic and diolefinic materials into streams of like components which comprises selectively extracting the monoolefins in a solvent from a stream containing saturates and monoolefins and recovering the saturated hydrocarbons and replacing the monoolefins from the extract by absorbing diolefins in the solvent to allow recovery of the monoolefins and subsequently separating the diolefins from the solvent.

More specifically, in this embodiment for separating Patented Jan. 11, 1972 parafiins, olefins and diolefins, a solvent is contacted in a first zone successively with three streams.

The first stream is a hydrocarbon stream comprising light Weight olefins such as a C olefin and light weight saturated hydrocarbons such as propane.

The second stream is a hydrocarbon stream comprising intermediate weight olefins such as Q, olefins and intermediate weight saturated hydrocarbons such as butane.

The third stream is a hydrocarbon stream comprising light weight, intermediate weight and medium weight olefins such as isoamylene, and medium weight saturated hydrocarbons such as pentanes.

From this first zone there is separated an overhead raffinate comprising substantially saturated hydrocarbons, that is, propane, butane and pentane. There is also separated an extract comprisnig substantially the solvent and the olefins.

This extract from the first zone is then passed on con tact with a fourth hydrocarbon stream comprising medium weight olefins such as isoamylene, medium weight saturated hydrocarbons, such as pentanes, and medium weight diolefins, such as isoprene, and there is separated overhead the previously defined third hydrocarbon stream and an extract comprising the solvent and the diolefins.

The extract is passed to any suitable separation means from which the diolefins are recovered and the solvent is recycled to the first zone if desired.

A portion of the third hydrocarbon stream is introduced into the first zone as previously described. Another portion is passed to any suitable separation means by which the desired separation of the C olefins, C olefins and isoamylenes is made.

Hence, there is recovered from the overhead fraction a stream comprising primarily parafi'ins, from the intermediate fraction, a stream comprising primarily monoolefins, and from the bottoms fraction, a stream comprising primarily diolefins.

In a second embodiment of this invention, the process is adapted to the separation of aromatics, cycloparaffins and paraffins from their admixtures. In this embodiment, the first stream contacted by the solvent can comprise benzene, cyclohexane and hexane, the second stream would contain toluene, methylcyclohexane and heptane; the third stream would contain xylene, dimethylcyclohexanes and octanes.

The first stream separated would contain the C C and C paraffins; the second stream separated would contain the C C and C cycloparafiins and the third stream upon separation of the solvent would contain the aromatics.

In each embodiment, it is seen that by contacting the plurality of hydrocarbons successively in order of their increasing carbon content with a solvent which has an increasing afiinity for those hydrocarbons with a lower hydrogen to carbon content, there is separated a first stream having the geneeral formula of C H a second stream having the general formula C H and a third stream comprising hydrocarbons having hydrogen and carbon in a mol ratio of less than 2.

Hence, it is an object of this invention to provide a more economical solvent extraction process.

It is another object of this invention to provide a solvent extraction process in which a plurality of contiguous boiling materials can be separated in a minimum number of zones.

These and other objects of this invention will be clear from the following disclosure.

In general, this invention is applicable to any solvent extraction process which involves removal of one or more components from a mixture by selective absorption by a solvent, the removal being based upon the ab- 3 sorptive affinities of the various components in the solvent.

In its more practical aspects, however, the invention is applicable to the C to C range of saturates, monoolefins and diolefins to affect separation into more easily fractionated streams of C to C saturates, C C and C olefins, and C and C diolefins.

Generally, solvent extraction is conducted within zones through which the solvent and hydrocarbon are passed in countercurrent contact at suitable temperatures and at a pressure sufiicient to maintain the solvent and hydrocarbons in the liquid phase. Suitable solvents include acetonitrile, furfural, methyl carbitol, and sulfolane. Hydrocarbons, to which the invention applies, include streams containing paraflins, olefins, diolefins and the like, containing up to about six carbon atoms. For purposes of discussion, the example given is limited to a stream containing hydrocarbons having from three to five carbon atoms including paraffins and olefins, without meaning to limit the invention thereto.

Referring now to the attached drawing, which illustrates one embodiment of this invention, there are shown extraction zones 1 and 2 and fractionation zones 3 and 4, heat suppliable to zones 3 and 4, by means not shown, to effect separation and recovery of the various materials.

Into zone 1, through conduit is introduced a C cut comprising a paraffin and an olefin. Below the introduc tion point of the C cut, through conduit 11 is introduced into zone 1 a C cut comprising paraffins and olefins. Into the upper portion of zone 1, above the point of introduction of the C cut thereinto, a solvent is introduced through conduit 12, the solvent being introduced from a source subsequently discussed. The solvent passes downward, countercurrently to the ascending hydrocarbon streams with a first raffinate stream being recovered overhead through conduit 13 and an extract stream being recovered from the bottom of zone 1 through conduit 14.

The stream recovered from zone 1 through conduit 13 will contain predominately those paraffinic hydrocarbons 4 3. In zone 3, conventional fractionation is made to separate a C and C olefin overhead fraction through conduit 18, a C olefin fraction, substantially free of parafiins, being taken from the bottom of the zone through conduit 19.

The solvent, having passed downward through zone 2 and having absorbed some portion of diolefins, is routed through conduit 20 into fractionation zone 4. Here, there is produced an overhead cut, comprising principally diolefins, which is routed through conduit 21 into zone 2 as reflux, a cut comprising principally isoprene which is taken through conduit 22, and a substantially hydrocarbon-free, or lean, solvent which is routed back to zone 1 through conduit 12, a portion being introduced into zone 2 through conduit 23 if desired.

The following example will serve to indicate the operation of the process in which the invention was employed to facilitate isoprene recovery. Numbers designate the same streams, conduitsand zones as employed in the previously-discussed flow diagram.

Zone 1, the olefin extractor, was 11 feet 6 inches in diameter and contained 100 sieve trays on suitable spacing. It was operated at a temperature of 130 F. and a pressure of about 225 p.s.i.a.

Solvent, comprising methyl carbitol and sulfolane, was introduced into zone 1 at its top at a rate of about 1,165,000 pounds per hour.

A C and a C stream were introduced into zone 1 on its 10th and 31st trays, respectively, numbering from the bottom of the zone.

Stream 16, a portion of stream 17, the overhead from zone 2, was introduced into the lower section of zone 1.

Approximate analyses of the various streams around zone 1 are given in the following table. These analyses are typical, and are meant only to illustrate the operability and effectiveness of the process rather than to indicate a material balance for the process. Relatedly, while some water can be employed with the solvent, none is shown introduced through conduits 10 and 11 which are miniin these data.

TABLE I Stream No.

Overhead Identification analysis, 03 feed from Reject Tower 1 pounds/hr. Solvent stream Zone 2 parafiins bottoms C parafiin 6, 600 680 6, 110 C3 olefin. 4, 610 6, 282 295 C4 parafii 10 663 5, 722 C4 olefin 400 8, 269 366 C5 parafiin 3, 286 365 G5 monoolefin 54, 820 37 C4 and O diolefins 131, 410 Solvent 57, 650 1, 157, 650

mally absorbed in the solvent. In addition, it will contain the principal portion of those parafl inic hydrocarbons introduced into zone 2, as hereinafter explained.

Into zone 2, through conduit 15, is introduced a C cut comprising paraffins and olefins. Into the upper portion of zone 2 through conduit 14 is introduced that extract stream from zone 1. Additional fresh solvent can be introduced through conduit 23. These streams pass in countercurrent contact, the solvent extracting from the C cut the more soluble components. Inasmuch as the preferential solubility of the hydrocarbons in the solvent employed varies decreasingly from diolefins to olefins, and thence to parafiins, some portion of the diolefins entering zone 2 with the C cut will displace some portion of the olefins in the extract introduced through conduit 14, with the result that some portion of the olefins extracted in zone 1 pass overhead from zone 2 and into zone 1 through conduit 16. Accordingly, from conduit 16, some portion of these olefins is taken as a side cut into fractionation zone Zone 2, the diolefin extractor, was 13 feet in diameter and contained sieve trays on suitable spacing. It was operated at a temperature of 130 F. and a pressure of about 130 p.s.i.a.

The bottoms stream 14 from zone 1 was introduced into the upper section of zone 2. A combined C cut was introduced through conduit 15. Introduction of these streams into zone 2 was made on trays 130 and 50, respectively. No solvent was introduced from conduit 12 through conduit 23. The overhead from zone 4 was introduced through conduit 21 into the lower portion of zone2 as reflux. After countercurrent contact between the streams, the raffinate stream was taken overhead through conduit 17, as previously discussed, a portion being routed through conduit 17 to zone 3 which serves to fractionate C and C olefins from C olefins.

The solvent and extracted hydrocarbons were removed from the lower section of the zone and routed to zone 4 through conduit 20.

Approximate analyses of the aforementioned streams related to the operation of zone 2 are as given below in Table II.

TABLE II Stream N0.

Extract to tower 4 Tower 4 Identification analysis, pounds/hr. food overhead A portion of that stream taken overhead from zone 2 through conduit 17 was routed to zone 3 where it was fractionated to produce an overhead stream through conduit 18 and a bottoms stream through conduit 19. The analyses of these streams is given below.

That stream taken from the bottom of zone 2 through conduit 20 was routed to zone 4 where it was fractionated to yield the solvent stream recycled through conduit 12 and that stream removed through conduit 22. Analyses of these streams from zones 3 and 4, not previously set forth, are given in Table 111.

Cs parafiin- Ca monoolefin...

Solvent The above data indicate that the process of this invention is operable to effect hydrocarbon separations and indicate that this separation can be effected when introducing a plurality of heterogeneous streams to a minimum of extraction zones.

A review of these data indicate that a predominance of the saturated paraffins were recovered as nonextracted, rejected parafiinic materials in stream 13.

Relatedly, a predominance of the unsaturated parafiins were recovered as extractable olefins in stream 17 which was then simply fractionated to produce the C and lighter olefin cut of conduit 18 and the heavier C monoolefin cut of conduit 19.

Similarly, a predominance of the more unsaturated C diolefins were recovered as extractable olefins in streams 22 having been separated by simple fractionation from the solvent which was returned to zone 1.

In some cases feedstream 11 might contain appreciable amounts of butadiene. In this event the butadiene would be recovered together with isoprene in stream 22. The mixture of butadiene and isoprene is easily separated by fractionation.

Hence, it will be seen that the method of this invention lends itself to the simultaneous separation of a plurality of contiguous boiling fractions into their components distinguishable upon the basis of their saturation, in a minimum of equipment without requiring complete separation of the contiguous boiling fractions and without requiring an individual and separate solvent for each fraction.

It will be appreciated that modifications can be made to the method for carrying out the invention. For example, the extraction zones can be established as one continuous tower in which the extractive steps take place in different sections thereof. However, such are considered as being within the skill of the art.

What is claimed is:

1. A process for separating olefins, diolefins and saturated hydrocarbons from a plurality of streams comprising mixtures thereof which comprises:

(a) passing a solvent in a first zone in successive contact with a first hydrocarbon stream comprising light weight olefins and light weight saturated hydrocarbons and with a second hydrocarbon stream comprising intermediate weight olefins and intermediate weight saturated hydrocarbons, and with a third hydrocarbon stream comprising light weight olefins, intermediate weight olefins and medium weight olefins and medium weight saturated hydrocarbons and separating a first rafiinate comprising substantially saturated hydrocarbons and a first extract comprising substantially said solvent and said olefins;

(b) passing said first extract in contact with a fourth hydrocarbon stream comprising medium weight olefins, medium weight saturated hydrocarbons and di olefins and separating said third hydrocarbon stream and a second extract comprising solvent and diolefins;

(c) passing a portion of said third hydrocarbon stream to said first zone;

((1) passing a portion of said third hydrocarbon stream to separating means and separating said olefins; and

(e) passing said second extract to separating means and recovering said diolefins.

2. The process as defined in claim 1 in which the first hydrocarbon stream comprises essentially propane and its homologs, the second hydrocarbon stream comprises essentially butane and its homologs and the fourth hydrocarbon stream comprises essentially pentane and its homologs and the fourth hydrocarbon stream comprises essentially pentane and its homologs.

3. The process as defined in claim 1 in which the solvent is selected from the group consisting of acetonitrile, furfural, methyl carbitol and sulfolane.

4. The process as defined in claim 1 in which solvent is recycled to the first zone from the separating means from which the diolefins are recovered.

5. The process as defined in claim 1 in which the parafiins, olefins and diolefins contained in said hydrocarbon streams contain up to about six carbon atoms.

6. The process as defined in claim 1 in which the solvent and hydrocarbon streams are passed in said first zone in countercurrent contacting relationship.

7. The process as defined in claim 1 in which the olefins of said third hydrocarbon stream are separated by fractionation.

8. The process as defined in claim 1 in which a solvent is passed in successive contact with a C cut, a 0.; cut and a third hydrocarbon stream, there being separated a first rafiinate comprising substantially C C and C parafiins and a first extract, said first extract being passed in contact with a fourth hydrocarbon stream, there being separated a third hydrocarbon stream from which olefins are recovered and a second extract stream from which diolefins are recovered.

DELBERT E. GANTZ, Primary Examiner C. E. SPRESSER, 1a., Assistant Examiner US. Cl. X.R.

208-321; 260-674 SE, 677 A 

